Policy-based Message Scheduling Using FlexRay

This paper proposes a virtual communication layer for time triggered networks, enabling a policy-based message scheduling as well as preemption which in turn simplifies real-time verification. The introduced layer is particularly advantageous in the automotive domain since it reduces the complexity of scheduling time-triggered communication systems and simplifies incremental changes of existing schedules. We propose a framework to schedule event-triggered messages based on a predefined policy in time-triggered communication slots, improving the network utilization while logically separating messages from different devices. Furthermore, we enhance the versatility of the system, allowing to transmit data that exceeds the size of one time-triggered slot. The proposed policy-based scheduling with fixed priorities enables the integration of mixed criticality applications in time-triggered networks, while ensuring hard deadline constraints. A prototypical implementation is provided for FlexRay, complying with the existing protocol and, thus, making it possible to coexist with the standard transmission scheme. Our experimental results demonstrate the advantages of the virtual layer, showing an increase in flexibility and significantly lower message latencies in case of asynchronous communication.